Liquid level control means



May 20, 1952 H. M. STAGGS ET AL LIQUID LEVEL CONTROL MEANS 4 Sh'eets-Sheet 2 Filed Oct. 25. 1947 QTTEST W&M: IW

INVENTORS HoraceM Sia yys By Louis Z'Davz's flu 5 KJ flizorng May 20, 1952 H. M. STAGGS ET AL 2,597,198

7 LIQUID LEVEL CONTROL MEANS Filed on. 23. 1947 4 Sheets-Sheet 3 May 20; 1952 H. M. STAGGSETAL 2,597,198

LIQUID LEVEL CONTROL MEANS Filed Oct. 23, 1947 4 Sheets-Sheet 4 HZTEST INVENTORS HoraceMSZayys 1 klil/ Patented May 20, 1952 LIQUID LEVEL CONTROL MEANS Horace M. Staggs and Louis F. Davis, Dallas, Tcx., assignors to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Application October 23, 1947, Serial No. 781,582

19 Claims.

This invention relates to improvements in liquid level control means.

More specifically, it involves means for controlling the level of the liquid within a tubing string or conductor of an oil well, the reservoir pressure of which is insufficient to raise the liquid to the well surface, the purpose being to assure lifting of the liquid to the well surface with the aid of auxiliary fluids, for example, air or gas, having maximum available pressures.

In those wells in which the reservoir pressure is insufficient to raise the liquid to the well surface, it is common practice to lift the liquid to the well surface by the injection within the column of liquid of an auxiliary fluid, the point of injection of the auxiliary fluid being within limits dependent upon the normal maximum level of the liquid and the pressure of the fluid. There are on the market a number of known devices for periodically injecting fluid into the column of the well liquid. One such device is commonly termed an intermitter device, and more specifically is described in United States patent to H. M. Staggs, No. 1,683,930, dated September 11, 1928, entitled Air Lift Pump. Another such device is described in United States patent to R. O. Walton, No. 2,385,316, dated September 18, 1945, entitled Well Flow Device. Still another such device is described in United States patent to J. D. Nixon, No. 2,405,232, dated August 6, 1946, entitled System and Apparatus for Flowing Wells. 1

These and other similar devices are being commercially employed with satisfactory results. However, they will at times fail to operate when, for example, due to a sporadic increase in reservoir pressure, the hydrostatic pressure of the liquid is increased in excess of the maximum available fluid pressure. The purpose of the present invention, therefore, is to control the hydrostatic pressure or level of the liquid within a tubing string or well conductor relative to fluid pressure and within the limits of the maximum available fluid pressure, and thereby to insure at. all times the operation of the particular lifting means. Various modifications of this invention will be hereinafter described in combination with the intermitter device described in the Staggs patent, No. 1,683,930 above mentioned. It will be apparent, however, that its use is equally ap plicable in combination with the well flow devices shown in the patent to Walton No. 2,385,316, and the patent to Nixon, No. 2,405,232, and other similar devices.

One of the objects of this invention, therefore, is to provide a liquid level control means for accurately controlling the level of liquid within a tubing string or conductor of an oil well, the reservoir pressure of which is insuflicient to raise the liquid to the well surface.

Another object of the invention is to provide liquid level control means which may be automatically actuated by the application of auxiliary fluid under pressure, and which automatically will be actuated by alternating differentials between the pressure of the auxiliary fluid and the hydrostatic pressure of the liquid within the tubing string, to admit liquid from the well reservoir into the tubing string or well conductor until a predetermined level of the liquid in the tubing string or conductor has been reached, and when this has been accomplished, to seal off the tubing string or conductor against the admission of additional liquid from the reservoir.

Another object of the invention is to provide a liquid level control means adaptable for use in combination with the intermitter means for controlling the level of the well liquid within the tubing string or conductor of an oil well whereby operation of the intermitter means will at all times be assured.

Other objects of the invention will be apparent from the description and claims which follow:

In the drawing like numerals are used to indicate like parts.

Figure 1 is an elevational view, partly in section, of a well structure showing generally the combination of an intermitter device and the device of the present invention.

Figure 2 is an enlarged elevational view, partly in section, showing the intermitter device.

Figure 3 is a sectional view along line 3--3 of Figure 2.

Figure 4 is a sectional view taken along line 4-4 of Figure 2.

Figure 5 is an elevational view, partly in section, showing one form of the present invention.

Figure 6 is an elevational view partly in section showing a modified form of the invention shown in Figure 5, and in which the valve is closed against the admission of additional liquid from the tubing string. 7

Figure '7 is a view like Figure 6 with the exception that the valve is shown in an open position.

Referring to the drawings, and in particular to Figure 1 thereof, the numeral l represents generally an oil well comprising casing 2, and tubing or conductor 3 secured within casing 2 by conventional means at wellhead 4. The well I is produced from reservoir 5 through perforations 6, the liquid entering casing 2 from reservoir 5 being directed into tubing 3 by packer I. Intermitter 8, and liquid level control means 9 are built into tubing 3 and are actuated in a manner hereinafter described, by auxiliary fluid under pressure in annular space Ill between casing 2 and tubing 3. Fluid under pressure is admitted into annular space H) through pipe H from a source not shown.

The intermitter device shown in Figures 1, 2, 3, and 4, of the drawings comprises generally housing I2 secured at its opposite ends to tubing 3 by threaded couplings l3 and in which valve 14 is mounted for slidable movement within sleeve l5 secured within axial bore [5 in housing 12 by threaded collar ll. Valve I4 is seated, as at I8, and is normally maintained in a closed position by the action of helical spring IS-distended between shoulder of housing [2 and shoulder 2! of cap 22 threaded to stem 23 of valve |4. Fluid'underpressure in annular space 10 is fnormalli maintained against the pressure side of valve '14, through interconnecting port 24 and chamber 25. However, upon opening of the valve l4, the fluid under pressur will be caused to pass throughinterconnecting ports 26, 21, 28, and '2 9, and axial bore 30, sealed against chamber 25 by threaded cap SI, and into the liquid in the space of tubing 3 generally designated by the "number 32, from 'which'space it will rise through vertical bores or "ports 33in housing 12, and into the body of liquid in the space of tubing 3 generally designated by th numeral 34. Valve I4 is mechanically'operated intermittently by the lowering'of weight '35 against cap 22, the action of weight35 being controlled through the medium 'of wire line3'B and lowering and raising mechanism 31 locatedat the well surface.

At such times as the volume of liquid above intermitter B, that is, in the space of tubing 3 generally designated by the numeral 34 is proportionate to the pressure of the fluid, the fluid upon entering such body of liquid will cause the liquid to"b'e'co'me aerated, and thereafter it will lift'the liquid to the well surface. However, at such times as the volume of well liquid above intermitter 8 is increased in'relation to the pressure of the fluid due, for example, to a sporadic increase in reservoir pressure, the intermitter is said to have failed to function because of insufficient fluid pressure to lift the aerated body of liquid tothe well surface. The present invention is'designed to prevent these failures by at all times controlling the maximum level of the well liquid aboveintermittert.

The liquid level control means shown in Figure 5 of the drawings comprises generally a housing 38 formed of sections 39, 40, and 4|, interconnected by threaded couplings 42 and 43, and a valve 44, the action of which is controlled through the mediumof 'a piston 45. The liquid level control means is threaded as at 45, to tubing 3, ate point below intermitter 8, and at its lower end is provided with the conventional strainer 41.

Valve 44 is normally maintained in a closed position by the action of helical spring 48, distended'between shoulder 49 of housing section 4 I, and shoulder 50of 'cap 5| threaded to valve stem 52, and fixedly secured thereto by locknut 53. Valve 44 is seated, as at 54, against valve sleeve 55, secured within housing section 4| by threaded collar 56. Movement of valve 44 against the act qn'o in 4.8 i on roll d bypiston 4.5. pro.-

vided with sealing rings 51 and mounted for slidable movement within cylinder 58, threaded as at 59 within housing section 39, and in a manner to provide annular space 69 therebetween and housing section 40. Fluid under pressure in the annular space between casing 2 and tubing 3 is at all times directed through open ports 6! and 62 against head 630i piston 45, and in the operation of the liquid level control means it will be seen that the well liquid is at all times directed against head 84 of piston 45, the pressure thereagainst being dependent upon the hydrostatic pressure of the liquid in the tubing string above the liquid level control means. Therefore, upon release of liquid pressureagainst head 64, for example, due to operation of intermitter 8, it will be seen thatpiston 45 will be caused to be moved downwardly against nut 53 by the presence of the fluid against head '63, whereby valve 44 will be forced to an open position against the action of spring 43. Valve 44 having been opened, the well'liquid within tubing 3 below the valve will flow under reservoir pressure upwardly through chambe'r 65, ports 68, and '61, into section 40 of housing 33, through annular space Elthrough port'fit, and into the tubing above the liquid level control means. The liquidentering the tubing above-the liquid level control means will rise above the intermitter device through ports 33 and will continue to do so until al ev'el is reached at which a sufficient hydrostatic press'ure will be developed whereby the pressure against head '64 of piston 5, with the aid of spring43will reverse the pressure differential across'piston'45, thereby causing piston 45 to rise and valve 44 to become'clo'sed by th action of spring '48. The valve44,once it is closed, will remain closed until further'operation of intermitter 8, at which time the pressure differential across piston 45 will again be i reversed and the cycle repeated.

Theinven'tion as exemplified in Figures '6 and 7 diifers from that shown in Figure 5 principally in the use of a bellows '69 in lieu of piston 45 'for opening valve '44. More particularly, th device shown in Figures 6 and 7, comprises genera'lly'a housing formed ofend sections 10 and II threaded at 72 and 13, respectively, to central section 74, and at 15 and 1-5, respectively, totubm s. Valve 44 is seated, asat I1,on seat memberlt, rigidly secured within housing section 1!, by

threaded collar 19, 'Which collar 19 also serves as a guide sleeve to valve stem 52, through axial bore 80, and to provide a series of verticalbores or ports 8!, for the passage of liquid therethrough. Valve 44 is normally maintained in a closed position by helical spring 43 distended between flanged collar 82 and nut 83 threaded "on the free end of stem 52, and rigidly secured there'- on by locknut 84. Bellows 69 is secured by'w elding or in any other suitablemanner, as at '85,t'o floating head '36 and, as at 87, to fixed 'head 88, the fixed head '88 bein'grigidly secured as -by threading at 89 m the one end of cylinder 90 which in turn is threaded at its opposite end at 9|, to flanged member 92 of end section 19, and in a manner providing sealed bellowscham'ber 83 and annular space 94 therebetween'and the inner wall of'central'section 14. Bellows stem '95 is threaded at 96 'to bellows head '86, and adjacent and from the'inte'rior of bellows 69. CapHH, is

threaded at I02, to the free end ot'bellowss'tem 95 and upon compression of bellows 09 will be caused to move downwardly with stem 95 against cap I03, and through the medium of stem 52 to open valve 49. It will be seen that when bellows 69 is in a distended position, cap IOI is brought to rest against cap I03, but that liquid within space I04 within central section member 14 is at all times fre to flow into and from the interior of bellows 99 through openings I05 in cap NH, and ports I and annular groove I06 in cap 98. It furthermore will be seen that opening movement of valve 44, and consequently the compression of bellows 159 is limited by cap I01 threaded at I08 into end section II.

Upon opening of valve 44, liquid entering through strainer I09 will be caused to flow by reservoir pressure through openings H0 in cap I01, past valve 44, through ports 8|, into space I04 in central member 14, and through annular space 94, and from which it will follow through interconnecting ports I I l and I I2 and into tubing 3 above the liquid level control means, and consequently, to a predetermined level above intermitter 8 in the manner hereinbefore described. Also the well liquid entering the liquid level control means will be caused to enter the interior of bellows 69 through ports I05 and I00 and annular groove I06 and thus to exert a pressure against the interior of bellows 69 dependent upon the level of the liquid in tubing 3 above the liquid level control means, as against the pressure of v the fluid in the annular space [0 which at all times is applied against the exterior of bellows 09 through interconnecting ports I I3 and I I4 providing communication between the annular space I0 and bellows chamber 93.

Upon operation of intermitter 8, a differential in pressure across the bellows 69 in favor of the pressure of the fluid in the annular space I0 will be brought about, whereby bellows 69 will be compressed and cause bellows stem 95 to be moved in a downwardly direction against cap I03 and valve stem 52, thereby causing valve 44 to be opened and to admit additional liquid to tubing 3 to the predetermined level at which time the differential in pressure across bellows 69 will be reversed in favor of the pressure of the liquid against the interior of the bellows, and the valve 44 closed.

We claim:

1. In a well in a producing reservoir having a pressure insufiicient to flow the well liquid to the well surface including a casing, a tubing within the casing, and means for directing the well liquid into the tubing, means positioned within the tubing for controlling the level of the well liquid within the tubing, comprising valve means normally preventing the flow of liquid therethrough, a source of fluid pressure, and pressure responsive means responsive alternately to the fluid pressure and to the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure responsive means being operable upon the application of fluid pressure to open the valve and to maintain the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure sufficient to operate the pressure responsive means against the action of the fluid pressure and to permit the valve to close.

2. In a well in a producing reservoir having a pressure insumcient to flow the well liquid to the well surface and including a casing, a tubing within the casing, and means for directing the well liquid into the tubing, means positioned within the tubing for controlling the level of well liquid within the tubing, comprising valve means normally preventing the flow of liquid therethrough, a source of fluid pressure, pressure responsive means responsive alternately to the fluid pressure and'to the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure responsive means being operable upon the application of the fluid pressure to open the valve and to maintain the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure offsetting the applied fluid pressure, and means for closing the valve.

3. In a well in a producing reservoir having a pressure insufficient to flow the well liquid to the well surface and including a casing, a tubing within the casing, and means for directing the well liquid into the tubing, means positioned within the tubing for controlling the level of well liquid within the tubing, comprising valve means normally preventing the flow of liquid therethrough, a source of fluid pressure, and pressure responsive means movable in one direction by the application of fluid pressure and in the opposite direction by the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure responsive means opening the valve upon the application of fluid pressure and maintaining the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure sufficient to operate the pressure responsive means against the action of the fluid pressure and to permit the valve to close.

4. In a well in a producing reservoir having a pressure insufiicient to flow the well liquid to the well surface and including a casing, a tubing within the casing, and means for directing the well liquid into the tubing, means positioned within the tubing for controlling the level of well liquid within the tubing, comprising valve means normally preventing the flow of liquid therethrough, a source of fluid pressure, and pressure responsive means responsive alternately to the fluid pressure and to the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure responsive means comprising a floating piston member movable in one direction by the application of fluid pressure to open the valve and to maintain the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure suflicient to move the floating piston in the opposite direction thereby permitting the valve to close.

5. In a well in a producing reservoir having a pressure insufficient to flow the well liquid to the well surface and including a casing, a tubing within the casing, and means for directing the well liquid into the tubing, means positioned within the tubing for controlling the level of well liquid within the tubing, comprising valve means normally preventing the flow of liquid therethrough, a source of fluid pressure, pressure responsive means responsive alternately to the fluid pressure and to the hydrostatic pressure of the liquid the level of which is to be controlled and operable upon application of the fluid pressure to open the valve and maintain the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure sufficient to operate the pressure responsive means against the action of the fluid pressure and to permitthe valve to close, the pressure responsive means comprising a normally distended bellows,

means for applying the fluidpressure externally of the bellows, and means for-applying the hydrostatic pressure internally of the bellows.

6. In a well ina. producing.:reservoir, having a pressure insufficient to :flow' the well liquid tothe well surface and "including a casing, a tubing within the casing, and means for directing the well liquid into the "tubing, means positioned within the tubing for controlling the level ofwell liquid'within the tubing, comprising valve means normally preventing the Iflow of .liquidthere through, a source of fluid pressure, and pressure responsive means responsive alternatelytothe fluid pressure and to the hydrostatic pressure of the liquid the level of which is to :be controlled, the pressure responsive means comprising anormally distended bellows, means operably associating the bellows'with the valve; means for applying the fluid pressure externally of the bellows whereby the bellows isxcontracted thereby :opening the valve and maintaining the valve inan open position until: passage therethroughrof :a quantity of liquid providinga hydrostatic pressure greater than the fluid pressure, and ;means for applying the hydrostatic pressure internally of thebellows wherebythe bellows will be caused to return to its normally distended position, thereby permitting the valve to close.

7. In a well in a producing reservoir having a pressure insufiicient to flow the well liquidto the well surface, including a casing, a tubing within the casing, means for directing the Well liquid into the tubing, and means operable periodicallyv and independently of the liquid level in the tubing for lifting the well liquid to the surface of the ground; the combination of means for controlling the level of well liquid within the tubing,. comprising valve means normally positioned to prevent the flow of liquid therethrough, a source of fluid pressure, andpressure responsive Imeans responsivealternately to the fluid. pressure and to the hydrostatic pressure of the liquid, the level of which is to be controlled, thepressure responsive-means being operableupon the application of the fluid-pressure toopen the valve and to maintain the valve in an open position: until passage therethrough-of a quantity ofliquidprovidinga hydrostatic pressure sufficient to operate the pressure responsive means; against the action of the fluid pressure and to permit the valve to close.

8. Ina well in, a producing reservoirhaving .a pressure insufficient to flowthe well liquid to. the well surface, including, a casing, a tubingwithin the casing, means for'directing the well liquid into the tubing, and means operable periodically and independently of the liquid level in the. tubing for lifting the well liquid to the surface of the ground; the combination of means for controlling the level of well liquid within the tubing, comprising valve means normally positioned to prevent the flow of liquid therethrough, a source of fluid pressure, pressure responsive means responsive alternately to the fluid pressure and to the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure-responsive means being operable upon the application of the fluid pressure to open the valve and to maintain the valve in an open, position until passage therethrough of a. quantity of liquid pro.- viding a hydrostatic pressure offsetting the applied fluid' pressure, and means for closing the valve. 7

9. In a wellin a producing reservoir having a pressure insufficient to flow the well liquidto the Well surface, including a casing, a tubing within the casing, means for directing the well liquid into the tubing, and means operable periodically and independently of the liquid level inthe tubing for lifting the well liquid to the surface of the ground; the combination of means for controlling the level of well liquid within the tubing, comprising valve means normally positioned to prevent the flow of liquid therethrough, a source of fluid pressure, and pressure responsive means movable in one direction by the application of fluidpressure and in the opposite direction by the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure responsive means opening the valve upon the application of "fluid pressure and maintaining the valvewin an open position until passage therethroughof a quantity of liquid providing a hydrostatic pressure suf ficient to operate the pressure responsive means against the action of the fluidxpressure and to permit the valve to close.

10. In a well producing reservoir having a pressure insufiicient to flow the xwellgliquid to the well surface, including a casing, a tubing within the casing,,means for directing the well liquid into the tubing, and "means operable vperiodically and independently of the liquid level in the tubing for lifting the well liquid to the. sure face of the ground;-the combination of -means for controlling the level of well liquid within the tubing, comprising valve means normally positioned to prevent the flow of liquid therethrough, a source of fluid pressure,v and pressure responsive means responsive alternately to the-fluid pressure and to the hydrostatic pressure ofthe liquid the level of which'is'to'be controlled, :the pressure responsive means 'comprisinga floating piston member movable in-one direction by the application of the fluid pressure to-open-thevalve and to maintain the valve inan open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure sufficient to move the floating piston in theopposite-directicn thereby permitting the valve to close.

11. In a well in a producing reservoir having a pressure insufficienttoflow the well liquid tQ.the well surface, including a casing,- a tubing within the casing, means for'directing the :well liquid into the tubing, and means operable periodically and independently of the liquid level 'inthetubing for lifting the well liquid to the surface'of the ground; the combination of means for controlling the level of well liquid within the tubing, comprising valvemeans normally positioned to prevent the flow of liquid therethrough, a source of fluid pressure, pressure responsive means responsive alternately to the fluidlpressure and to the hydrostatic-pressure of the, liquid thelevel of which is to be controlledand operable upon applicationof the fluid pressure to open the valve and maintain the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure surficient to operate the pressure responsive-means against the action of the fluid pressure and to permit the valve to close, the pressure responsive means comprising a normally distended bellows, means for applying the fluid pressureexternally of the bellows, and means for applying the hydrostatic pressure internally of the bellows.

12. In a well in a producingresorvoir having a-pressure insufiicient to flow thewell liquidjto the well surface, including a casing, a,-. tubing within'the casing, means for directinglthe well liquid into the tubing,- and meansgoperable 7pc.-

riodically and independently of the liquid level in the tubing for lifting the well liquid to the surface of the ground; the combination of means for controlling the level of well liquid within the tubing, comprising valve means normally positioned to prevent the flow of liquid therethrough, a source of fluid pressure, pressure responsive means responsive alternately to the fluid pressure and to the hydrostatic pressure of the liquid the level of which is to be controlled, the pressure responsive means comprising a normally distended bellows, means operably associating the bellows with the valve, means for applying the fluid pressure externally of the bellows whereby the bellows is contracted thereby opening the valve and maintaining the valve in an open position until passage therethrough of a quantity of liquid providing a hydrostatic pressure greater than the fluid pressure, and means applying the hydrostatic pressure internally of the bellows whereby the bellows will be caused to return to its normally distended position thereby permitting the valve to close.

13. The combination with a well tubing having an intermitter control valve connected therein and operable independently of the liquid level in the tubing for controlling the admission of a lifting fluid under pressure into said well tubing, of a liquid level control device connected in said well tubing below said intermitter valve and having means for maintaining the level of the well liquids at a desired point in said tubing.

14. The combination as set forth in claim 13, wherein the liquid level control device includes a main valve which is normally closed to shut 01f upflow of the well liquids through the tubing, and means actuated when the liquid level in said tubing falls below a predetermined point for opening said valve to allow upflow of the well liquids in said tubing, said last means also functioning when the desired liquid level is restored to close the main valve.

15. A liquid level control device including a well tubing, a housing connected with the tubing provided with a flow passage communicating with the tubing whereby well liquids will flow upwardly through the passage and the tubing, a valve in the passage movable to open and closed position for controlling the upward flow of the liquids in the tubing, biasing means tending to close said valve, a source of fluid pressure, and means in fluid connection with, and responsive alternately to, the fluid pressure and the hydrostatic pressure of the liquid in the tubin for opening the valve when the level of liquid in the tubing falls below a predetermined high point and for permitting said biasing means to close the valve when the level of liquid in the tubing again reaches such high point.

16. The combination with a well conductor having an intermitter control valve connected therein and operable independently of the liquid level in the conductor for controlling the admission of a lifting fluid under pressure into said well conductor, of a liquid level control device connected in said well conductor below said intermitter valve and having means for maintaining the level of the well liquids at a desired point in said conductor.

I 17. The combination with a well conductor having an intermitter control valve connected therein and operable independently of the liquid level in the conductor for controlling the admission of a lifting fluid under pressure into said well conductor, of a liquid level control device connected in said well conductor below said intermitter valve and havin means for maintaining the level of the well liquids at a desired point in said conductor, wherein the liquid level control device includes a main valve which is normally closed to shut 01f upfiow of the well liquids through the conductor, and means actuated when the liquid level in said conductor falls below a predetermined point for opening said valve to allow upflow of the well liquids in said conductor, said last means also functioning when the desired liquid level is resorted to close the main valve.

18. An apparatus for flowing wells comprising, a well conductor, an intermitter control valve connected in the conductor and operable independently of the liquid level in said conductor for controlling the admission of a pressure lifting fluid into the conductor at predetermined time intervals, a liquid level control device connected in the conductor below said intermitter valve and having valve means for shutting ofi the admission of well liquid into the conductor when the level of said liquid rises to a predetermined point in the conductor.

19. A liquid level control device including a well tubing, a housing connected with the tubing provided with a flow passage communicating with the tubing whereby well liquids will flow upwardly through the passage and the tubing, a pressure actuated valve normally maintained in a closed position in the passage for controlling the flow of the liquids in the tubing, a source of fluid pressure, and means responsive alternately to the fluid pressure and to the hydrostatic pressure of the liquids in the tubing for controlling the operation whereby the valve will be opened when the level of the liquids in the tubing falls below a predetermined high point and closed when the level of the liquids in the tubing again reaches such high point.

HORACE M. STAGGS. LOUIS F. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENT Number Name Date 1,585,732 Otto May 25, 1926 1,780,808 Archer Nov. 4, 1930 1,812,361 Nicholson June 30, 1931 2,002,791 Otis May 28, 1935 2,006,909 Boynton July 2, 1935 2,261,364 Grove Nov. 4, 1941 

